Molten metal injector system and method

ABSTRACT

The molten metal injector system includes a holder furnace, a casting mold supported above the holder furnace, and a molten metal injector supported from a bottom side of the mold. The holder furnace contains a supply of molten metal. The casting mold defines a mold cavity for receiving molten metal from the holder furnace. The injector projects downward into the holder furnace and is in fluid communication with the mold cavity. The injector includes a cylinder defining a piston cavity housing a reciprocating piston. The piston pumps molten metal upward from the holder furnace to the mold cavity. The cylinder further includes a molten metal intake for receiving molten metal into the piston cavity. The intake may be a valve or an aperture defined in the sidewall of the cylinder.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of U.S. applicationSer. No. 09/609,997, filed Jul. 3, 2000, which claims the benefit ofU.S. Provisional Application Serial No. 60/142,218, filed Jul. 2, 1999,and entitled “Molten Metal Injector System” and No. 60/142,315, filedJul. 2, 1999, and entitled “Valveless Molten Metal Injector System”.

STATEMENT REGARDING FEDERALLY FUNDED RESEARCH

[0002] The subject matter of this application was made with UnitedStates government support under Contract No. 86X-SU545C awarded by theDepartment of Energy. The United States government has certain rights tothis invention.

BACKGROUND OF THE INVENTION

[0003] 1. Field of the Invention

[0004] The present invention relates to a molten metal injector systemand, more particularly, to a molten metal injector system suitable foruse with molten aluminum and aluminum alloys for producing metalcomponents.

[0005] 2. Description of the Prior Art

[0006] The manufactures of ground transportation vehicles, such asautomobiles, sport utility vehicles, light trucks, vans, buses andlarger capacity trucks, have made major efforts in recent years toreduce vehicle weight. Weight reductions reduce harmful atmosphericemissions and increase fuel efficiency of ground transportationvehicles. Presently, a majority of the body components for groundtransportation vehicles are formed from individual steel components thatare assembled via resistance spot welding. For example, the floor panframe of an automobile is normally constructed from a number ofindividual steel stampings that are spot welded together. It would beadvantageous to produce body components for ground transportationvehicles, such as the floor pan frame of an automobile, as a singlecasting made of lighter weight material such as aluminum. As a result,the costs associated with producing multiple steel stampings and thenassembling the stampings may be eliminated. The same technology wouldalso be suitable for components in the aerospace industry.

[0007] There are several known methods for producing component castings,examples include: high pressure cold chamber vacuum die casting, premiumsand casting, a level pour process practiced by Alcoa, Inc. forproducing components for the aerospace industry and low pressure hotchamber injection. Low-pressure hot chamber injection is particularlywell suited for producing components made from non-ferrous metals havinga low melting point, such as aluminum, brass, bronze, magnesium andzinc.

[0008] A typical casting arrangement known in the prior art for castingmolten metals includes the use of a supply tank configured to containmolten metal and a cylinder partially submerged in the tank. Thecylinder typically has a connection at its base to an injectionpassageway that leads from the tank to a casting die located outside thetank. The casting die is most often located adjacent the tank. Thepassageway leading from the cylinder is typically inclined or exhibits a“goose neck” configuration. A piston reciprocates in the cylinder tomove the molten metal into the injection passageway and, ultimately, thecasting die.

[0009] The reciprocating piston located in the cylinder is typicallyconfigured to inject or pump the molten metal into the injectionpassageway during its downstroke, and allows molten metal to be drawninto the cylinder during its upward return stroke. Numerous examples ofthe foregoing are known in the prior art such as from U.S. Pat. No.;2,655,699 to Morin; U.S. Pat. No. 3,106,755 to Moor; U.S. Pat. No.3,123,875 to Madwed; U.S. Pat. Nos. 3,234,605 and 3,239,896 both toThompson; U.S. Pat. No. 3,652,073 to Louis; U.S. Pat. Nos. 3,999,593 and4,085,791 both to Kaiser; U.S. Pat. No. 4,423,763 to Perrella; and U.S.Pat. No. 4,749,021 to Nakano. The disclosures of the foregoingreferences each share a common characteristic: the use of areciprocating piston that injects molten metal into an inclined orgoose-necked passageway leading to a casting die located laterallyadjacent to a holding furnace or supply tank. Other prior art in thisarea includes U.S. Pat. No. 3,300,822 to Thompson; U.S. Pat. No.4,210,196 to Weiner; and U.S. Pat. No. 5,660,223 to Chieman et al.

[0010] The use of reciprocating pistons that inject molten metal into ainclined or goose-necked passageway that leads to a casting die duringthe downstroke of the piston are known to have a tendency to disturb themetal oxide film surface of the molten metal contained in the holdingfurnace or supply tank. Consequently, undesirable metal oxides and/orair bubbles are often injected into the casting mold along with themolten metal, resulting in an inferior casting. Metal oxides are alsoknown to form in the piston cylinder during the downstroke of thepiston. The present invention provides a molten metal injector systemthat corrects these deficiencies found in the prior art.

[0011] Accordingly, it is an object of the present invention to providean apparatus and method for the casting of inexpensive metal components,particularly those made from aluminum and aluminum alloys. In addition,it is an object of the present invention to provide an improvedapparatus and method for casting metal components that overcomes thedeficiencies generally found in the prior art, such as those describedhereinabove.

SUMMARY OF THE INVENTION

[0012] The above objects are accomplished with a molten metal injectorsystem according to the present invention. The molten metal injectorsystem in accordance with the present invention includes a holderfurnace, a casting mold, and a molten metal injector. The holder furnacecontains a supply of molten metal. The casting mold is supported abovethe holder furnace and has a bottom side facing the holder furnace. Thecasting mold defines a mold cavity for receiving molten metal from theholder furnace. The molten metal injector is supported from the bottomside of the casting mold and projects into the holder furnace. Theinjector is in fluid communication with the mold cavity and includes acylinder defining a piston cavity housing a reciprocating piston. Thepiston is configured to pump molten metal upward from the holder furnaceand inject molten metal into the mold cavity. The piston and cylinderare at least partially submerged in molten metal when the holder furnacecontains molten metal. The cylinder further includes a molten metalintake for receiving molten metal into the piston cavity. The piston isoriented substantially perpendicular to the bottom side of the castingmold and is movable through a downstroke and a return stroke. The intakeis configured to open during the return stroke of the piston and permitmolten metal to flow into the piston cavity. During the downstroke, thepiston is configured to pump the molten metal received into the pistoncavity upward to the casting mold and inject the molten metal into themold cavity.

[0013] A molten metal filter may cover the molten metal intake forfiltering molten metal flowing into the piston cavity through the moltenmetal intake.

[0014] The injector may include a lifting mechanism connected to thebottom side of the casting mold and operatively connected to the pistonfor moving the piston through the downstroke and return stroke. Thelifting mechanism may be a rack and pinion.

[0015] The molten metal intake may be a valve configured to open duringthe return stroke of the piston and permit inflow of molten metal intothe piston cavity, and further configured to close during the downstrokeof the piston and prevent inflow of molten metal into the piston cavity.

[0016] The molten metal intake may be an aperture defined in a sidewallof the cylinder and permitting fluid communication between the pistoncavity and the molten metal contained in the holder furnace. Theaperture is configured during the return stroke of the piston for inflowof molten metal into the piston cavity. The aperture is furtherconfigured to be closed by the piston during the downstroke of thepiston to prevent inflow of molten metal into the piston cavity. Amolten metal filter may cover the aperture for filtering molten metalflowing into the piston cavity through the aperture.

[0017] The piston and cylinder are preferably made of materialscompatible with molten aluminum or molten aluminum alloys.

[0018] The cylinder may define a fill conduit for placing the pistoncavity in fluid communication with the mold cavity. The fill conduitpreferably extends along an axis substantially parallel to the piston.

[0019] The present invention is also a method of operating a moltenmetal injector in connection with a supply molten metal and a castingmold having a mold cavity. The method may include the steps of:providing a supply of molten metal; providing a molten metal injector,with the molten metal injector including a cylinder defining a pistoncavity housing a reciprocating piston, with the cylinder having a moltenmetal intake for receiving molten metal from the supply of molten metalinto the piston cavity, and with the piston movable through a downstrokeand a return stroke by a lifting mechanism operatively connected to thepiston; supporting the injector above the supply of molten metal suchthat the cylinder and piston are at least partially submerged in thesupply of molten metal, and such that the molten metal intake liescompletely submerged in the supply of molten metal; moving the pistonthrough a return stroke with the lifting mechanism; permitting inflow ofmolten metal from the supply of molten metal into the piston cavitythrough the molten metal intake during the return stroke of the pistonsuch that the piston cavity is at least partially filled with moltenmetal; moving the piston through a downstroke with the liftingmechanism; and preventing inflow of molten metal from the supply ofmolten metal into the piston cavity with the piston during thedownstroke of the piston.

[0020] The method may further include the steps of: locating a castingmold above the supply of molten metal such that a bottom side of thecasting mold faces the supply of metal; supporting the injector from thebottom side of the casting mold; and placing the piston cavity in fluidcommunication with the mold cavity such that during the downstroke ofthe piston molten metal received into the piston cavity through themolten metal intake is injected into the piston cavity.

[0021] The piston may be oriented substantially perpendicular to thebottom side of the casting mold and the cylinder may define a fillconduit for placing the piston cavity in fluid communication with themold cavity. The fill conduit may extend along an axis substantiallyparallel to the piston, such that during the downstroke of the pistonmolten metal received into the piston cavity is moved vertically upwardthrough the fill conduit and injected into the mold cavity.

[0022] Further details and advantages of the present invention willbecome apparent from the following detailed description read inconjunction with the drawings, wherein like parts are designated withprimed reference numerals.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a partial cross-sectional side view of a molten metalinjector system according to the present invention;

[0024]FIG. 2 is a front cross-sectional view of an injector for themolten metal injector system of FIG. 1 according to a first embodimentof the present invention;

[0025]FIG. 3 is a side cross-sectional view of the injector of FIG. 2;

[0026]FIG. 4 is a top plan view of the injector of FIG. 2;

[0027]FIG. 5 is a cross-sectional view of an injector for the moltenmetal injector system of FIG. 1 according to a second embodiment of thepresent invention;

[0028]FIG. 6 is a cross-sectional view of an injector for the moltenmetal injector system of FIG. 1 according to a third embodiment of thepresent invention;

[0029]FIG. 7 is a partial cross-sectional side view of a casting moldand the injector used in the molten metal injector system of FIG. 1;

[0030]FIG. 8 is a side view of the molten metal injector system of FIG.1 having multiple injectors in accordance with the present invention;and

[0031]FIG. 9 is a cross-sectional plan view taken along lines IX-IX inFIG. 8, and

[0032]FIG. 10 is a cross-sectional view of an injector for the moltenmetal injector system of FIG. 1 according to a fourth embodiment of thepresent invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0033]FIG. 1 shows a molten metal injector system in accordance with thepresent invention and designated with reference numeral 10. The injectorsystem 10 generally includes a holder furnace 12 that contains a supplyof molten metal 14, such as a molten aluminum alloy, a casting mold 16positioned above the holder furnace 12, and at least one injector 18supported from the casting mold 16. The molten metal 14 contained in theholder furnace 12 may be exposed to the atmosphere and a metal oxidefilm surface 20 will form at the top of the molten metal 14 contained inthe holder furnace 12. Alternatively, the holder furnace 12 may furtherinclude a cover (not shown) such that the molten metal 14 is enclosedwithin the holder furnace 12. The holder furnace 12 is in fluidcommunication with a main melter furnace 22, which typically contains alarge quantity of the molten metal 14 while the holder furnace 12contains a much smaller quantity of molten metal 14. For example, themain melter furnace 22 may contain 30,000 pounds of the molten metal 14while the holder furnace 12 may contain about 2,000 pounds of the moltenmetal 14. The main melter furnace 22 maintains a steady supply of themolten metal 14 to the holding furnace 12 during operation of theinjector system 10. When the molten metal 14 is a containment-difficultmolten metal, such as molten aluminum alloys, the holder furnace 12 ispreferably lined with refractory material 24 such as Sigma or BETA IIcastable refractory material products manufactured by Permatech.

[0034] The casting mold 16 is supported by a support surface 26, such asthe floor of a structure. The casting mold 16 is configured for castingultra large, thin-walled components such as those that may be used inground transportation vehicles. An ultra large, thin-walled componentpart for a ground transportation vehicle may have dimensions approaching3 meters long, 1.7 meters wide and 0.4 meters in depth, and the castingmold 16 will be configured accordingly. The casting mold 16 ispreferably suitable for use with molten metal alloys having a lowmelting point, such as aluminum alloys. The casting mold 16 includes aholder frame 28 that is supported on the support surface 26. The supportsurface 26 is positioned a sufficient distance above the holder furnace12 so that at least portions of the injector 18 lie above the metaloxide film surface 20 of the molten metal 14 contained in the holderfurnace 12. For example, the support surface 26 and, hence, the castingmold 16 may be eighteen inches above the metal oxide film surface 20 ofthe molten metal 14 when the holder furnace 12 is filled with the moltenmetal 14.

[0035] The casting mold 16 includes a lower die 30 and an upper die 32,which together define a mold cavity 34. A cover plate 36 is positionedon top of the upper die 32. A top clamp plate 38 is separated from thecover plate 36 by a spacer block 40. Hoist rings 42 are preferablyattached to the top clamp plate 38 for mold removal and installation. Abottom side 44 of the casting mold 16 faces the holder furnace 12.

[0036] In a preferred embodiment of the present invention, a pluralityof the injectors 18 is supported from the bottom side 44 of the castingmold 16 and project downward into the holder furnace 12. However, inFIG. 1 only one injector 18 is shown for clarity and expediency inexplaining the present invention. The use of multiple injectors 18 tocast an ultra large, thin-walled component will be discussed herein withreference to FIGS. 7-9.

[0037] FIGS. 1-4 show the details of the injector 18 according to afirst embodiment of the present invention. The injector 18 includes acylinder 46 for submerging in the molten metal 14 contained in theholder furnace 12. The cylinder 46 defines a piston cavity 48 and a fillconduit 50 in fluid communication with the piston cavity 48. Thecylinder 46 includes a lower end 52 that is submerged in the moltenmetal 14 contained in the holder furnace 12 when the holder furnace 12is filled with the molten metal 14. At the lower end 52 of the cylinder46, the cylinder 46 defines a tapered inner surface 54. In particular,the tapered inner surface 54 is formed at the lower end 52 of thecylinder 46. The cylinder 46 includes a sidewall 56 having an innersurface 57.

[0038] A piston 58 is positioned in and movable within the piston cavity48. The piston 58 has substantially the same diameter as the pistoncavity 48 and, the tapered inner surface 54 has a slightly largerdiameter than the piston 58. In particular, the piston 58 is movable ina reciprocating manner within the piston cavity 48 through a downstrokeand a return stroke. FIG. 2 illustrates the piston 58 at a substantiallyfull downstroke position in solid lines, and illustrates a full returnstroke position of the piston 58 in broken lines. At the substantiallyfull downstroke position of the piston 58, the piston 58 preferablyremains in contact with the inner surface 57 of the cylinder 46 andprevents inflow of molten metal 14 into the piston cavity 48 at thelower end 52 of the cylinder 46. The total distance the piston 58 mayextend downward may be controlled by a PLC (programmable logiccontroller) controlling the servomotors powering the lifting mechanismattached to the piston 58, as discussed hereafter. During the returnstroke position of the piston 58, the piston 58 may close off the fillconduit 50 from the piston cavity 48 as illustrated in broken lines inFIG. 2. The cylinder 46 and the piston 58 are preferably made of amaterial compatible with molten aluminum alloys. In particular, suitablematerials for the cylinder 46 and the piston 58 include graphite andhigh quality ceramic compounds, such as Sialon and Si₃N₄. Additionally,other suitable materials compatible with molten aluminum alloys includeblends of ZrO₂ and BN. Further, the present invention envisions the useof both graphite and high quality ceramic compounds for the cylinder 46and the piston 58.

[0039] Preferably, the piston 58 is oriented substantially perpendicularto the bottom side 44 of the casting mold 16. Hence, during thedownstroke of the piston 58, the piston moves in a direction away fromthe bottom side 44 of the casting mold 16, and during the return strokeof the piston 58 it moves upward toward the bottom side 44 of thecasting mold 16. A fill tube 61 is connected to the fill conduit 50 by aconnecting flange 62 and passes through the bottom side 44 of thecasting mold 16. In particular, the fill tube 61 extends through avertical opening in the holder frame 28 and the lower die 30. The filltube 61 places the piston cavity 48 in fluid communication with the moldcavity 34. The fill tube 61 may be made of materials similar to thoseused for the cylinder 46 and the piston 58.

[0040] The piston 58 is movable through the downstroke and the returnstroke by a lifting mechanism 64 that is fixed to the cylinder 46 by theconnecting flange 62, which is also used to connect the fill tube 61 tothe fill conduit 50. The lifting mechanism 64 is preferably a rack andpinion as shown, but may also be a chain drive. With the cylinder 46substantially submerged in the molten metal 14 contained in the holdingfurnace 12, the lifting mechanism 64 is located above the metal oxidefilm surface 20 of the molten metal 14. In particular, the liftingmechanism 64 is preferably located about fourteen inches above the metaloxide film surface 20 of the molten metal 14 contained in the holderfurnace 12 when the holder furnace 12 contains the molten metal 14. Thelifting mechanism 64 and, hence, the injector 18 are fixed to the bottomside 44 of the casting mold 16 by an upper flange 66. The liftingmechanism 64 may be connected to the upper flange 66 by mechanicalfasteners (i.e., bolts). Similarly, the upper flange 66 may be fixed tothe bottom side 44 of the casting mold 16 by mechanical fasteners (i.e.,bolts). Thus, the injector 18 is attached to the lower die 30 of thecasting mold 16 via the flange 66 and structural connections between theflange 66 and the connecting flange 62.

[0041] Due to the close proximity of the lifting mechanism 64 to theholder furnace 12, the lifting mechanism 64 is subjected to hightemperatures and is preferably made of a material capable ofwithstanding temperatures on the order of 600-1000° F. Suitablematerials for the lifting mechanism 64 include those previouslydiscussed that are compatible with molten aluminum alloys, as well assteel and other ferrous materials since the lifting mechanism 64 doesnot directly contact the molten metal 14. The rack and pinion comprisingthe lifting mechanism 64 may be driven by a remotely controlledservomotor (not shown). The servomotor may be controlled by a PLC. ThePLC may be programmed to adjust the vertical distance the piston 58 maytravel during its downstroke.

[0042] A valve 68 is connected to the cylinder 46 for receiving themolten metal 14 into the injector 18. Hence, the valve 68 operates asthe molten metal intake to the injector 18. The valve 68 is preferablyconnected to the cylinder 46 such that with the cylinder 46 at leastpartially submerged in the molten metal 14 contained in the holdingfurnace 12, the valve 68 is completely submerged in the molten metal 14and located below the metal oxide film surface 20 of the molten metal14. In particular, in a preferred embodiment of the injector 18 thevalve 68 is located about fourteen inches below the metal oxide filmsurface 20 of the molten metal 14, when the holder furnace 12 is filledwith the molten metal 14.

[0043] The valve 68 is in fluid communication with the piston cavity 48and is configured to open at the beginning of the downstroke of thepiston 58 and close during the return or pumping stroke of the piston58. The valve 68 preferably opens fully when the piston 58 begins itsdownstroke and closes fully when the piston 58 reaches its substantiallyfull downstroke piston. The valve 68 remains closed during the return orpumping stroke of the piston 58, thereby sealing off the piston cavity48.

[0044] The opening and the closing of the valve 68 is controlled by avalve controller 69. The valve controller 69 may be a rack and pinionoperatively connected to the valve 68. The rack and pinion forming thevalve controller 69 may be driven by a remotely controlled servomotor.

[0045] A molten metal filter 70 may be used to cover the inlet to thevalve 68 to filter and remove debris from the molten metal 14 flowinginto the piston cavity 48 through the valve 68. In addition to moltenmetal filtration, the molten metal filter 70 may additionally serve toregulate the flow of molten metal 14 into the piston cavity 48 so thatthere is no initiation of turbulent molten metal flow into the pistoncavity 48.

[0046] The lifting mechanism 64 controlling the piston 58 may be set toallow the piston 58 to form a gap with the tapered inner surface 54 ofthe cylinder 46, which permits the molten metal contained in the pistoncavity 48 to drain from the piston cavity 48 when it is time to performroutine maintenance on the injector 18, or replace the injector 18.

[0047]FIG. 5 shows a second embodiment of the injector according to thepresent invention and designated with reference numeral 18′. Theinjector 18′ shown in FIG. 5 is substantially identical to the injector18 shown in FIGS. 1-4, but now the valve 68 is omitted from the injector18′. The molten metal intake to the piston cavity 48′ is now definedentirely by a gap 71 formed between the piston 58′ and the tapered innersurface 54′ of the cylinder 46′ when the piston 58′ is extended to thesubstantially full downstroke position. The size of the gap 71 may beadjusted by adjusting the lifting mechanism 64′, which controls thevertical distance the piston 58′ may travel with respect to the cylinder46′. Accordingly, in the injector 18′, at the substantially fulldownstroke of the piston 58′, the piston 58′ extends below the end ofthe cylinder 46′ which permits the gap 71 to be formed between thepiston 58′ and the tapered inner surface 54′ of the cylinder 46′. Thepiston land of the piston 58′ may also be shortened to facilitateformation of the gap 71 between the piston 58′ and the tapered innersurface 54′ of the cylinder 46′.

[0048] In FIG. 5, the piston 58′ is shown at a full downstroke positionwhere the gap 71 is approximately at a maximum and the rate of inflow ofmolten metal into the piston cavity 48′ through the gap 71 would beapproximately at a maximum. A molten metal filter 70′ may be attached tothe lower end 52′ of the cylinder 46′. For example, the molten metalfilter 70′ may be provided as a sleeve extending downward sufficientlyfrom the lower end 52′ of the cylinder 46′ such that the piston 58′ mayextend downward to its full downstroke position. The molten metal filter70′ is used to filter the molten metal 14 and further, may be used toregulate the flow of molten metal into the piston cavity 48′ so thatinitiation of turbulent molten metal flow into the piston cavity 48′through the gap 71 is minimized.

[0049]FIG. 6 shows a third embodiment of the injector according to thepresent invention and designated with reference numeral 18″. Theinjector 18″ shown in FIG. 6 is substantially identical to thepreviously discussed injectors 18, 18′, but further includes twoapertures 72 formed in the sidewall 56″ of the cylinder 46″. Theapertures 72 are formed adjacent the tapered inner surface 54″ of thecylinder 46″. The injector 18″ in FIG. 6 includes two apertures 72formed in the cylinder 46″, but it will be appreciated by those skilledin the art that at a minimum only one aperture 72 is necessary. Inaddition, the injector 18″ may have more than two apertures 72 inaccordance with the present invention.

[0050] The piston land of the piston 58″ is formed similar to the pistonland of the piston 58 for the injector 18 of FIG. 2. The apertures 72are each covered by a molten metal filter 70″ for filtering andstraining debris from the molten metal 14 as the molten metal 14 flowsthrough the apertures 72 and into the piston cavity 48″. The moltenmetal filter 70″ may be further used to regulate the flow of moltenmetal 14 into the piston cavity 48″ so that initiation of turbulentmolten metal flow into the piston cavity 48″ through the apertures 72 isminimal.

[0051] The apertures 72 are located in the sidewall 56″ of the cylinder46″ such that the apertures 72 are open for inflow of the molten metalinto the piston cavity 48″ when the piston 58″ is in the substantiallyfull downstroke position. The apertures 72 begin to open for inflow ofthe molten metal 14 into the piston cavity 48″ as the piston 58″approaches the substantially full downstroke position. At thesubstantially full downstroke position of the piston 58″, the piston 58″preferably remains in contact with the inner surface 57″ of the cylinder46″ and prevents inflow of molten metal 14 into the piston cavity 48″ atthe lower end 52″ of the cylinder 46″ when the piston reaches thesubstantially full downstroke position. Hence, the apertures 72 are themolten metal intake to the piston cavity 48″. As the piston 58″ beginsits return stroke, the outer circumferential edge of the piston 58″remains substantially engaged with the inner surface 57″ of the cylinder46″. The lifting mechanism 64″ may be adjusted to allow the piston 58″to extend below the end of the cylinder 46″ such that a gap forms whichprovides an egress point for molten metal when the injector 18″ requiresmaintenance or replacement.

[0052] Referring now to FIGS. 1-4, operation of the injector 18 througha downstroke and return stroke cycle of the piston 58 will now bediscussed. As stated previously, the injector 18 is supported from thebottom side 44 of the casting mold 16. The cylinder 46 and the piston 58are substantially submerged in the molten metal 14 contained in theholding furnace 12. As the piston 58 begins its downstroke, the valve 68opens and permits the molten metal 14 to flow into the piston cavity 48.As the piston 58 moves through its downstroke, the molten metal 14continues to flow into the piston cavity 48 through the valve 68 and themolten metal filter 70, if present.

[0053] After a predetermined period of time to allow the piston cavity48 to fill with the molten metal 14, the valve 68 closes and the liftingmechanism 64 is engaged to begin moving the piston 58 upward through itsreturn stroke. The piston 58 may be controlled such that the pistoncavity 48 may be entirely filled with molten metal 14 flowing throughthe valve 68 before the piston 58 reaches its substantially fulldownstroke position and before a gap forms between the piston 58 and thecylinder 46. The vertical distance traveled by the piston 58 iscontrolled by the lifting mechanism 64. The servomotors driving thelifting mechanism 64 and the valve controller 69 may be remotelycontrolled by a programmable logic computer (PLC) to control thedistance the piston 58 travels and the opening and closing of the valve68, as will be appreciated by those skilled in the art.

[0054] For example, a casting cycle may begin with the piston 58 at adownstroke position as shown in FIG. 2. At this point, the valve 68 isclosed, the piston cavity 48 is completely filled with molten metal 14,and the lifting mechanism's servomotor(s) controlled by the PLC beginsthe injection stroke (i.e., return stroke). This follows a pre-specifiedposition versus time path. When molten metal 14 fills the mold cavity34, pressure builds and the servomotor(s) can no longer follow a pathversus distance relation and abruptly changes to a torque holdingcondition. After the torque holding condition is established, whichreflects a pressure intensification of about 5 to 45 psi for asufficient time for the molten metal 14 to solidify in the mold cavity34, the valve 68 is opened and the piston 58 is slowly lowered to thestart position (i.e., downstroke position). The piston 58 may be set totravel any vertical distance required and is not limited to travelingbetween the full downstroke and full return stroke positions dependingon the application at hand, as will be appreciated by those skilled inthe art. In the case where no valve 68 is present, as shown in FIG. 5,the piston 58′ is lowered sufficiently for molten metal to enter intothe piston cavity 48′ through the gap 71.

[0055] Referring again to FIGS. 1-4, as the piston 58 moves upwardthrough its return stroke, the molten metal 14 now contained in thepiston cavity 48 is pumped upward by the piston 58 from the holderfurnace 12. The molten metal 14 flows through the fill conduit 50 andinto the fill tube 61. The molten metal 14 in the fill conduit 50 andthe fill tube 61 is injected under low pressure (i.e., less than about15 psi) into the mold cavity 34. As the piston 58 reaches thesubstantially full return stroke position, for example, the liftingmechanism 64 is stopped. The piston 58 may be stopped prior to the fullreturn stroke position if the torque holding condition occurs indicatingthat the mold cavity 34 is filled with the molten metal 14. A sensor(not shown) may be attached to the lifting mechanism 64 and used tosense when the piston 58 has reached the torque holding conditionindicating the mold cavity 34 is filled with the molten metal 14. Thesensor may be connected to the PLC controlling the lifting mechanism 64,for example.

[0056] The injector 18 of the present invention advantageously locatesthe valve 68 well below the metal oxide film surface 20 of the moltenmetal 14. Since the valve 68, (i.e., the molten metal intake) for theinjector 18, is located well below the metal oxide film surface 20, themetal oxide film surface 20 remains substantially undisturbed as themolten metal 14 from the holder furnace 12 flows into the piston cavity48 through the valve 68. As described previously, the valve 68 should belocated about fourteen inches below the metal oxide film surface 20.This assures that any disturbances to the metal oxide film surface 20are minimized and substantially prevents metal oxides from beingintroduced into the piston cavity 48 from the metal oxide film surface20.

[0057] In addition, because the piston cavity 48 is filled during thedownstroke of the piston 58 via the valve 68 this helps prevent theinitiation of turbulent molten metal flow and thus formation of metaloxides in the piston cavity 48 due to the action of the piston 58. Thedifficulty with many prior art piston arrangements is that the pumpingstroke of the piston is during the downstroke, which has a tendency todisturb the metal oxide film surface of the supply of molten metal inwhich the piston operates, as well as create disturbances within thepiston cavity which could cause metal oxides to form in the pistoncavity.

[0058] In the injector 18, the pumping stroke is the return stroke,which minimizes the chances of forming metal oxides in the piston cavity48, as well as minimizes the disturbances to the metal oxide filmsurface 20 of the molten metal 14 in the holder furnace 12. In addition,in the injector 18 the piston cavity 48 is gradually refilled during thedownstroke of the piston 58 with the molten metal 14 slowly enteringthrough the valve 68. The valve 68 permits the inflow of the moltenmetal 14 into the piston cavity 48 such that a vacuum is not generatedin the piston cavity 48 which could pull atmospheric air into the filltube 61 and the fill conduit 50 and further down into the piston cavity48. This substantially prevents the formation of metal oxides within thepiston cavity 48 due to the movement of the piston 58. A valve thatregulates the rate of inflow of the molten metal 14 into the pistoncavity may be used in place of the valve 68.

[0059] The injector 18 of the present invention may further include asource of inert gas 80, such as argon or nitrogen, in fluidcommunication with the fill tube 61. The source of inert gas 80preferably supplies the inert gas through the lower die 30 or the upperdie 32 and into the mold cavity 34. The inert gas 80 will flow down thefill tube 61 and fill conduit 50, and into the piston cavity 48. Thisprevents the introduction of atmospheric air into the fill tube 61, fillconduit 50, and the mold cavity 34, which could potentially form metaloxides in the piston cavity 48.

[0060] The injector 18′ of FIG. 5 operates in a substantially similarmanner to the injector 18 of FIGS. 1-4, with the exception that themolten metal 14 from the holder furnace 12 flows into the piston cavity48′ entirely through the gap 71 formed between the piston 58′ and thetapered inner surface 54′ of the cylinder 46′ at the substantially fulldown position of the piston 58′. Accordingly, the molten metal intake tothe piston cavity 48′, the gap 71, is located well below the metal oxidefilm surface 20 of the molten metal 14 in this embodiment, anddisturbances to the metal oxide film surface 20 of the molten metal 14are minimized.

[0061] The injector 18″ of FIG. 6 operates in a substantially similarmanner to the injector 18 of FIGS. 1-4 and the injector 18′ of FIG. 5,with the exception that with the piston 58″ located in the substantiallyfull downstroke position, the apertures 72 in the sidewall 56″ of thecylinder 46″ are open for inflow of the molten metal 14 into the pistoncavity 48″. The filters 70″ covering the apertures 72 act to filter andstrain debris from the molten metal 14 before passing through theapertures 72. As the piston 58″ begins its return stroke, the apertures72 begin to become closed-off by the piston 58″. In this embodiment,because the apertures 72 are located well below the metal oxide film 20,disturbances to the metal oxide film surface 20 are minimized.

[0062] As stated previously, the present invention envisions the use ofa plurality of injectors 18 (or 18′ or 18″) suspended from the bottomside 44 of the casting mold 16, as show in FIG. 8. Referring now toFIGS. 7-9, the injectors 18 are preferably supported from the bottomside 44 of the mold 16 to optimize the inflow of the molten metal 14into the mold cavity 34. FIG. 9 illustrates a possible configuration forarranging the injectors 18 to form a component piece for a groundtransportation vehicle, such as a single piece lift gate for a minivan.In the arrangement of FIG. 9, seven injectors 18 are utilized, with thelocations of the injectors 18 selected to optimize inflow of the moltenmetal 14 into the mold cavity 34 such that the molten metal 14 evenlyfills the mold cavity 34 without the introduction of occlusions that maybe formed by trapped air. The injectors 18 may be individuallycontrolled by a programmable logic controller, for example, such thatthe injectors 18 inject the molten metal 14 at different rates and atdifferent times as necessary to fill the mold cavity 34 to form thecomponent.

[0063]FIG. 10 shows a fourth embodiment of the injector according to thepresent invention and designated with reference numeral 18′″. Theinjector 18′″ shown in FIG. 10 is substantially similar to the injectors18, 18′, 18″ discussed previously, but is now configured to pump moltenmetal 14 upward to the mold cavity 34 during the downstroke of piston58′″ rather than during the return stroke of the piston 58′″. Inaddition, cylinder 46′″ includes a closed end 80. The molten metalintake for the injector 18′″ is now formed by at least one and,preferably, a plurality of apertures 82 formed at an upper end 83 ofcylinder 46′″. The apertures 82 may be covered by a molten metal filter70′″ in a similar manner to injector 18″ discussed previously inconnection with FIG. 6.

[0064] Cylinder 46′″ defines a piston cavity 48′″ having an innersurface 57′″. The cylinder 46′″ further defines a fill conduit 50′″,which is in fluid communication with the piston cavity 48′″. The fillconduit 50′″ cooperates with a fill tube 61′″, which extends through theholder frame 28 and cooperates with the mold cavity 34. As shown in FIG.10, the fill conduit 50′″ may extend up to the holder frame 28 andconnect to the fill tube 61′″ at this point. The cylinder 46′″ andpiston 58′″ may be made of materials similar to those discussedpreviously in connection with injectors 18, 18′, 18″.

[0065] The piston 58′″ is movable through a downstroke and a returnstroke by lifting mechanism 64′″. The lifting mechanism 64′″ ispreferably attached to the bottom side 44 of the holder frame 28. Thepiston 58′″ may further include a plunger ring 84, which forms thepistonhead of the piston 58′″. The lifting mechanism 64′″ may be a rackand pinion device controlled by servomotors as discussed previously.

[0066] The injector 18′″ of FIG. 10 preferably further includes a holderdevice 86 attached to the bottom side 44 of the holder frame 28. Theholder device 86 may be attached by conventional methods (i.e., bolts)to the bottom side 44 of the holder frame 28. The holder device 86connects to the upper end 83 of the cylinder 46′″ to support thecylinder 46′″ in the vertical direction. Thus, the injector 18′″ issupported against the bottom side 44 of the holder frame 28 in a similarmanner to the injectors 18, 18′, 18″ discussed previously.

[0067] Operation of the injector 18′″ differs from the operation of theinjectors 18, 18′, 18″ discussed previously. As stated previously, thepumping stroke of the piston 58′″ is its downstroke, and the fill strokeof the piston 58′″ is its return stroke. In particular, the piston 58′″permits inflow of molten metal 14 into the piston cavity 48′″ throughapertures 82 during its return stroke as the piston 58′″ approaches themetal oxide film surface 20 in the holder furnace 12. As shown in FIG.10, as the piston 58′″ moves upward and approaches its full returnstroke position, apertures 82 are open for inflow of molten metal 14into the piston cavity 48′″ to fill the piston cavity 48′″. When thepiston cavity 48′″ is full with molten metal 14, the lifting mechanism64′″ may be actuated to move the piston 58′″ downward through itsdownstroke. During its downstroke, the piston 58′″ closes-off theapertures 82 thereby preventing further inflow of molten metal 14 intothe piston cavity 48′″. As the piston 58′″ moves through its downstroke,molten metal 14 is forced from the piston cavity 48′″ into the fillconduit 50′″ and vertically upward into the fill tube 61′″ and,ultimately, into the mold cavity 34 of the casting mold 16 (not shown inFIG. 10).

[0068] In contrast to the prior art piston arrangements discussedpreviously, the cylinder 46′″ of the injector 18′″ includes a verticallyoriented fill conduit 50′″. The fill conduit 50′″ is arranged along anaxis substantially parallel to the piston 58′″. The vertical orientationof the fill conduit 50′″ permits the molten metal 14 contained in thepiston cavity 48′″ to be injected upward into the mold cavity 34 underpressure and against the force of gravity, which prevents or reduces theintroduction of atmospheric air into the molten metal 14. This minimizesthe formation of metal oxides and, further, the formation of pores orocclusions in the cast component when the molten metal 14 solidifies inthe mold cavity 34. The molten metal filter 70′″ attached to thecylinder 46′″ further aids in reducing the formation of metal oxides inthe piston cavity 48′″. Further, the piston 58′″ in the piston-cylinderarrangement of the injector 18′″ generally never reaches the metal oxidefilm surface 20 in the holder furnace 12 during its return stroke. Thus,the molten metal film surface 20 is typically undisturbed by thereciprocal movement of the piston 58′″.

[0069] A valve, such as a check valve, may be located in the apertures82 to permit inflow of molten metal 14 during the return stroke of thepiston 58′″, and prevent subsequent outflow of molten metal 14 from thepiston cavity 48′″ during the downstroke of the piston 58′″.Additionally, a valve arrangement such as that discussed previously inconnection with FIG. 2 may also be provided in the injector 18′″. Forexample the injector 18′″ may include a valve 68′″ in each of theapertures 82, with valves 68′″ configured to operate in a similar mannerto the valve 68′″ provided the injector 18 of FIG. 2.

[0070] The injector system of the present invention provides asimplified apparatus and method for casting inexpensive, but highquality metal components. The injector system of the present inventionmay be applied to cast complex components as a single piece, which couldbe used to replace stamping assemblies made from multiple stampedcomponents. In addition, the injector system of the present inventiongenerally overcomes the previously discussed deficiencies with the priorart. For example, the injector system in certain embodimentsadvantageously includes a piston that pumps molten metal during itsreturn stroke and permits inflow of molten metal to the piston cavityduring its downstroke. Another embodiment of the injector systemdescribed hereinabove includes a piston that pumps molten metal duringits downstroke, but does so in an improved piston-cylinder arrangementthat overcomes the deficiencies known in the prior art.

[0071] While preferred embodiments of the present invention weredescribed herein, various modifications and alterations of the presentinvention may be made without departing from the spirit and scope of thepresent invention. The scope of the present invention is defined in theappended claims and equivalents thereto.

We claim:
 1. A molten metal injector system comprising: a holder furnacefor containing a supply of molten metal; a casting mold supported abovethe holder furnace and having a bottom side facing the holder furnace,with the mold defining a mold cavity for receiving molten metal fromholder furnace; and a molten metal injector supported from the bottomside of the casting mold and projecting into the holder furnace, withthe injector in fluid communication with the mold cavity and including acylinder defining a piston cavity housing a reciprocating piston forpumping molten metal upward from the holder furnace and injecting moltenmetal into the mold cavity, wherein the piston and the cylinder are atleast partially submerged in molten metal when the holder furnacecontains molten metal, wherein the cylinder further includes a moltenmetal intake for receiving molten metal into the piston cavity, whereinthe piston is oriented substantially perpendicular to the bottom side ofthe casting mold and movable through a downstroke and a return stroke,wherein the intake is configured to open during the return stroke of thepiston and permit molten metal to flow into the piston cavity when theholder furnace contains molten metal, and wherein during the downstrokethe piston is configured to pump the molten metal received into thepiston cavity upward to the casting mold and inject the molten metalinto the mold cavity.
 2. The injector system of claim 1, furtherincluding a molten metal filter covering the molten metal intake forfiltering molten metal flowing into the piston cavity through the moltenmetal intake.
 3. The injector system of claim 1, wherein the injectorfurther includes a lifting mechanism connected to the bottom side of thecasting mold and operatively connected to the piston for moving thepiston through the downstroke and return stroke.
 4. The injector systemof claim 1, wherein the molten metal intake is a valve configured toopen during the return stroke of the piston and permit inflow of moltenmetal into the piston cavity and close during the downstroke of thepiston and prevent inflow of molten metal in the piston cavity.
 5. Theinjector system of claim 1, wherein the molten metal intake is anaperture defined in a sidewall of the cylinder permitting fluidcommunication between the piston cavity and the molten metal containedin the holder furnace, and wherein the aperture is configured during thereturn stroke of the piston for inflow of molten metal into the pistoncavity, and the aperture is further configured to be closed by thepiston during the downstroke of the piston preventing inflow of moltenmetal into the piston cavity through the aperture.
 6. The injectorsystem of claim 5, further including a molten metal filter covering theaperture for filtering molten metal flowing into the piston cavitythrough the aperture.
 7. The injector system of claim 1, wherein thepiston and the cylinder are made of materials compatible with moltenaluminum or molten aluminum alloys.
 8. The injector system of claim 3,wherein the lifting mechanism is a rack and pinion.
 9. The injectorsystem of claim 1, wherein the cylinder defines a fill conduit forplacing the piston cavity in fluid communication with the mold cavity,and wherein the fill conduit extends along an axis substantiallyparallel to the piston.
 10. An injector for injecting molten metal intoa mold cavity of a casting mold, comprising: a cylinder for at leastpartially submerging in a supply of molten metal, with the cylinderdefining a piston cavity, and with the cylinder defining a fill conduitin fluid communication with the piston cavity; a piston positionedwithin the piston cavity and movable through a downstroke and a returnstroke, with the fill conduit extending along an axis substantiallyparallel to the piston; a lifting mechanism fixed to the cylinder andoperatively connected to the piston for moving the piston through thedownstroke and the return stroke; and a valve connected to the cylinderfor receiving molten metal into the piston cavity when the cylinder andpiston are at least partially submerged in molten metal, wherein thevalve is configured to open during the return stroke of the pistonpermitting inflow of molten metal into the piston cavity when thecylinder and piston are at least partially submerged in molten metal,and wherein the valve is configured to close during the downstroke ofthe piston preventing inflow of molten metal into the piston cavity, andthe piston is configured to pump molten metal received into the pistoncavity into the fill conduit for injection into the mold cavity when thecylinder and piston are at least partially submerged in molten metal.11. The injector of claim 10, further including a molten metal filtercovering the intake to the valve for filtering molten metal flowing intothe piston cavity through the valve during the return stroke of thepiston.
 12. The injector of claim 10, wherein the piston and thecylinder are made of materials compatible with molten aluminum or moltenaluminum alloys.
 13. The injector of claim 10, wherein the liftingmechanism is a rack and pinion.
 14. An injector for injecting moltenmetal into a mold cavity of a casting mold, comprising: a cylinder forat least partially submerging in a supply of molten metal, with thecylinder defining a piston cavity and an aperture in a sidewall thereoffor receiving molten metal into the piston cavity, and with the cylinderdefining a fill conduit in fluid communication with the piston cavity; apiston positioned within the piston cavity and movable through adownstroke and a return stroke, with the fill conduit extending along anaxis substantially parallel to the piston; and a lifting mechanism fixedto the cylinder and operatively connected to the piston for moving thepiston through the downstroke and the return stroke, wherein theaperture is configured during the return stroke of the piston for inflowof molten metal into the piston cavity when the cylinder and piston areat least partially submerged in the molten metal, and wherein theaperture is configured during the downstroke of the piston to be closedby the piston, preventing inflow of molten metal into the piston cavity,and the piston is configured to pump molten metal received into thepiston cavity into the fill conduit for injection into the mold cavitywhen the cylinder and piston are at least partially submerged in themolten metal.
 15. The injector of claim 14, further including a moltenmetal filter covering the aperture for filtering molten metal flowinginto the piston cavity through the aperture during the return stroke ofthe piston.
 16. The injector of claim 14, wherein the piston andcylinder are made of materials compatible with molten aluminum or moltenaluminum alloys.
 17. The injector of claim 14, wherein the liftingmechanism is a rack and pinion.
 18. A method of operating a molten metalinjector in connection with a supply of molten metal and a casting moldhaving a mold cavity, comprising the steps of: providing a supply ofmolten metal; providing a molten metal injector, with the molten metalinjector including a cylinder defining a piston cavity housing areciprocating piston, with the cylinder having a molten metal intake forreceiving molten metal from the supply of molten metal into the pistoncavity, and with the piston movable through a downstroke and a returnstroke by a lifting mechanism operatively connected to the piston;supporting the injector above the supply of molten metal such that thecylinder and piston are at least partially submerged in the supply ofmolten metal, and such that the molten metal intake lies completelysubmerged in the supply of molten metal; moving the piston through areturn stroke with the lifting mechanism; permitting inflow of moltenmetal from the supply of molten into the piston cavity through themolten metal intake during the return stroke of the piston such that thepiston cavity is at least partially filled with molten metal; moving thepiston through a downstroke with the lifting mechanism; preventinginflow of molten metal from the supply of molten metal into the pistoncavity with the piston during the downstroke of the piston.
 19. Themethod of claim 18, further comprising the steps of: locating a castingmold above the supply of molten metal such that a bottom side of thecasting mold faces the supply of molten metal; supporting the injectorfrom the bottom side of the casting mold; and placing the piston cavityin fluid communication with the mold cavity such that during thedownstroke of the piston molten metal received into the piston cavitythrough the molten metal intake is injected into the mold cavity. 20.The method of claim 19, wherein the piston is oriented substantiallyperpendicular to the bottom side of the casting mold and the cylinderdefines a fill conduit for placing the piston cavity in fluidcommunication with the mold cavity, with the fill conduit extendingalong an axis substantially parallel to the piston, such that during thedownstroke of the piston molten metal received into the piston cavity ismoved vertically upward through the fill conduit and injected into themold cavity.